Infections in man and animals by influenza virus, a negative strand RNA virus, remain a serious disease problem. Our goal is to develop new influenza virus vaccines and to explore--in general--novel antiviral approaches. In the past, negative strand viruses were refractory to genetic manipulation using recombinant DNA techniques. However, this situation has been changed by our recent development of a system which allows site-specific mutagenization of the influenza virus genome and the expression, amplification and packaging of foreign genes into influenza virus. We now wish to use this technology to engineer stable attenuated influenza viruses for possible development as live virus vaccines. Changes in the coding sequences as well as in the region of the regulatory signals will be examined. In addition, we hope to express foreign genes by stable chimeric influenza viruses and to develop a general gene expression vector based on influenza virus. Other avenues concern the expression of ribozymes in tissue culture. These molecules possess RNA cleavage activity and attempts will be made to target them at influenza (m)RNAs in order to inhibit replication of these viruses. Another antiviral approach involves the use of oligonucleotides and their phosphorothioate derivatives. Sequence- specific and sequence-independent inhibitory effects of these compounds will be studied. Attempts will also be made to select drug-resistant mutants and to identify the resulting mutations in the viruses.